The 31-year-old beat Su Jeong Jang, ranked 231 in the world, 7-6 (7-4) 4-6 6-3 in Tuesday's final contest on the schedule.
In the first match since her second-round elimination to Belgian veteran Elise Mertens at the US Open, world No. 122 Tomljanovic dropped serve five consecutive times in the late-night humidity.
But she came good in the final set, winning four games on the spin to establish a firm hold at 4-0.
"I'm happy to be through, hopefully I will play a bit better in the next one," she said.
The former finalist will need to as she now meets Brazilian No.3 seed Beatriz Haddad Maia.
"They were tough conditions - though for both," added Tomljanovic. "it was about weathering the storm and staying tough in the crucial moments."
Earlier, compatriot Priscilla Hon was beaten 7-5 6-4 by lucky loser Polina Kudermetova in six minutes shy of two hours in their first ever meeting.
The Russian, 34 spots higher than Hon in the world rankings at No.163, served fewer aces and had more double faults but converted four of her five break points as opposed to the Queenslander's two of five.
Elsewhere, Britain's 2021 US Open champion Emma Raducanu enjoyed a 7-6 (7-4) 7-6 (7-5) triumph over the United States' Peyton Stearns.
.— wta (@WTA) @EmmaRaducanu's winner 😮�💨#KoreaOpen pic.twitter.com/YYsW1yGbdkSeptember 17, 2024
"I'm proud to have made it through to the next round. It was tough. It was very humid, the ball was bouncing around a lot," Raducanu said after the topsy-turvy contest which featured 12 breaks of serve.
"I haven't played many matches in the last few months and Peyton, she's a really good player and on really good form. I'm really pleased."
Among other ties Hailey Baptiste defeated fellow American and 2017 US Open champion Sloane Stephens 7-6 (7-4) 6-2 and Amanda Anisimova of the US had an upset 6-3 7-6 (7-5) win over sixth-seeded Kazakh Yulia Putintseva.
With AP & PA.
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